So, Magpul makes these folding sights called the MBUS. The reasoning behind them appears to be that since backup sights are, you know, backup, then a light and inexpensive plastic unit should work just fine for the job.
Like pretty much everything Magpul makes, they've been a phenomenal sales success, as well they should be: A front-'n'-rear pair of MBUS sights costs less than most quality steel folding rear sights alone, and the rear sight by itself (if you have a fixed front like I do) is cheaper than even the relatively low-end and snag-prone Yankee Hill folding rear.
So now I find out that of course there's some Chinese company selling cheap plastic knockoffs of an already inexpensive plastic sight. And the packaging is such that an unscrupulous seller could pass them off as the real deal.
Folks, if you're at a gun show and that "Aimpoint" or "EOTech" or "Magpul" accessory is priced too good to be true, then it probably is. The fake problem is so bad with Aimpoints that they even have a whole "How To Spot A Fake Aimpoint" section on their web site...
BONUS!: Via email, "How to spot a bogus Loopie!"